smtpscan is a remote SMTP server version detector. It can be used to
guess which mail software is used on a remote server, that may hide its
SMTP banner.

smtpscan works by testing the remote SMTP server reaction, thanks to
tests defined in the tests (${PREFIX}/share/smtpscan/tests) file. Almost
all of those tests consists in weird SMTP request, whose answer is not
precisely defined in the corresponding RFCs. Some other times, they check
whether the remote SMTP server is simply RFC compliant. After each test,
remote server returns a SMTP Error Message. Fingerprints are made of
SMTP Error Messages corresponding to the tests.
